Production of itaconic acid



Patented Sept. 7, 1948 PRODUCTION OF ITAGONIC ACID Earl J. Roberts andJoseph A. Ambler, New

Orleans, La., and Alfred Laurence Curl, Winter Haven, Fla., assignors tothe United States of America as represented by the Secretary ofAgriculture No Drawing. Application September 10, 1946, Serial No.898,022

1 (Balm.

(Cl. M37) (Granted under the act of March 3, 1883, as amended April 30,1928; 370 0. G. 757) This application is made under the act of March 3,1883, as amended by the act of April 30, 1928, and the invention hereindescribed, if patented, may be manufactured and'used by or for theGovernment of the United States of America for governmental purposeswithout the payment to us of any royalty thereon.

This invention relates to the production of itaconic acid, being animprovement over the invention as disclosed and claimed in anapplication for patent, Serial No. 696,020 filed Sept. 10, 1946, byJoseph A. Ambler and Alfred Laurence Curl, entitled Production ofitaconic acid, and has among its objects a process of producing the acidin a simple and efllcient manner in nearly quantitative yields and in ahigh state of purity.

Esters of the itaconic acid are valuable compounds useful in theformation of various types of plastics.

In general, according to the invention, aconitic acid in aqueoussolution is decomposed to itaconic acid and carbon dioxide by heating inthe presence of a small quantity of an inorganic salt of aconitic acid,the decomposition equation being represented as follows:

H-CCOOH HCH (Heat) 1] C-COOH (inorganic salt of CCOOH CO;

I aconitic acid) H(|JCOOH H-(iJ-COOH Aconitic acid Itaconic acidAconitic acid may be decomposed to itaconic acid by heat alone. Forexample, evaporation on the steam bath or boiling at atmosphericpressure of an aqueous solution of aconitic acid results in a decreasein titratable acidity and in evolution of C02. The reaction when carriedout at atmospheric pressure is much too slow, however, for practicalproduction of the itaconic acid, and furthermore, the formed itaconicacid is in part either isomerized or polymerized, or both, due to thelong heating period required for complete decomposition of the aconiticacid. The rate of decomposition may be increased by heating above theboiling point of the water present using pressure, but even with quitehigh temperatures, the time required is yet long.

It has been found, according to the present invention, that the rate ofdecomposition is accelerated by the presence of an inorganic salt ofaconitic acid. The itaconic acid can be produced according to thepresent invention in nearly quantitative yields in a state of highpurity at temperatures of about C. in shorter periods of time than ifthe salt of the aconitic acid be not present, and can be producedwithout the formation of any of the isomer, citraconic acid. In someinstances, however, small quantitles of citraconic acid may be formed,but for some uses of the final product, the presence of this isomer, insmall amounts at least, along with the itaconic acid is not detrimentaland may be advantageous.

The addition of the inorganic salt of the aconitic acid is mostconveniently accomplished by the addition of a small amount of a basicin organic compound or neutralizing material to the aqueous solution ofaconitic acid, thereby to neutralize a part of the aconitic acid, thebasic inorganic compound ionizing in the aqueous solution to givecations in the solution thus forming soluble salts of the aconitic acid.This results in a decrease in acidity of the solution.

Many metallic cations, such as those of copper, zinc, mercury, potassiumand barium, are effective for the purpose of the invention. However,magnesium excepted, cations of the alkali earth metals, in particularcalcium, are preferred, in that the quantity required for maximumeifectiveness is small, and with most of them, no isomerization of theitaconic acid to the citraconic acid takes place. Use of magnesium andthe alkali metals results in accelerating isomerization. of the itaconicacid as well as accelerating decomposition of the aconitic acid to theitaconic acid.

The quantity of cation added should be small in order to neutralize onlya small part of the aconitic acid. The quantity can best be gaged bymeasurement of the pH of the resulting aqueous solution of the aconiticacid and formed salt. Generally speaking, the pH of the solution shouldbe raised to not more than 4, a range of from 1 to 4 being permissiblebut about 2 being p eferred.

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4 sugarcane products, as described, for example, in Patent No. 2,280,085and Patent No. 2,359,537, are used as the starting material. Example VIIillustrates the invention in particular as applied to these aconitates.

Example VII 60 grams of commercial grade alkali-earth aconitate,containing 15.8% calcium, 3.1% magnesium, and 59% aconitic acid, wasmade into a slurry with 210 grams of water and 30 grams of concentratedsulfuric acid, producing a mixture Conccntra- Quantity of Conversion oftion of aco- Babic basic inorpH Tempera- Conversion itaconic acid m i 1ganic com- 0mm resulting tum t to itaconic to citraconic fg pound addedpgmd added solution acid, per cent acid mg NaOH 114. 9 2. 66 140 100 26.

10 71. 8 2. 140 l00 Negligible.

l5 l2 1. 140 97. 5 D0.

The time for completion of the decomposition may be determined by notingthe cessation of evolution of CO2, and to obtain completion of thereaction, the time used should in any event extend until the evolutionof CO2 ceases.

The foregoing examples exhibit the invention as applied to substantiallypure aconitic acid which is partially neutralized by the added basicinorganic compound. The decomposition process is not necessarily solimited, however, since it is possible to decompose certain inorganicsalts of the aconitic acid to corresponding salts of itaconic acid andof citraconic acid. The salts of aconitic acid used should be mono or disalts, in which case, of course, the aconitic acid salt is yet dibasicor monobasic. Example V exhibits the invention as applied to such asalt.

Example V 1.126 grams of monosodium aconitate (equivalent to 1 gram ofaconitic acid) dissolved in 10 ml. of water (pH 3.3) was autoclaved at140 C. In 2 hours the aconitate was completely decomposed. From theresulting solution of monosodium dicarboxylates, 39 milligrams ofcitraconic acid formed by isomerization of the acid itaconate initiallyproduced was obtained.

Example VI illustrates the invention in which aconitic acid is firstconverted to a mono or di salt and the salt then decomposed to thecorresponding itaconates.

Example VI To a solution of 1 gram of aconitic acid in 10 ml. of waterwas added one-half the amount of calcium carbonate necessary toneutralize the acid and the carbon dioxide generated was removed undervacuum. The solution had a pH of 3.55 and contained a. mixture ofmonohydrogen and dihydrogen calcium aconitates. After autoclaving for 2hours at 140 C., no aconitates remained, and the solution contained amixture of neutral and acid calcium itaconates. No citraconate wasfound.

The foregoing examples deal with substantially pure aconitic acid andmono or di salts of such acid as the starting materials, and areincluded in the disclosure of the above-identifled application. Theinvention has a greater practical utility, however, if certainalkali-earth aconitates as they are obtained from SOrgO or having a pHof 2.0. This was heated in an autoclave at C. for 2 hours, after whichtime evolution of carbon dioxide had stopped, and the mixture had a pHof 2.6. Five grams of concentrated sulfuric acid was added and thecalcium sulfate precipitate was removed by filtration. From the filtrate0.63 gram of citraconic acid (2.4% theoretical yield) and 23.5 grams ofcrude itaconic acid (88.3% theoretical yield), melting at 159 to 162 C.and having a neutralization equivalent of 64.75 was obtained. After onerecrystallization the itaconic acid obtained melted at to 161.5 C. andhad a neutralization equivalent of 64.9 (theoretical is 65) By followingthe procedure of Example VII, the necessity of intermediately convertingthe naturally occurring aconitates to aconitic acid is avoided, sincethe itaconic acid is obtained directly, thus making the process lesscostly. The chemical process is, of course, essentially the same as inthe case of use of pure aconitic acid, since the sulfuric acid added tothe alkali-earth aconitates (in an amount slightly less than chemicallyequivalent to the cations present in the aconitate solution) firstreacts with a part of the aconitates to form freeaconitic acid andcertain insoluble sulfates (particularly calcium sulfate, since thenaturally occurring aconitates are principally calcium aconitate), whichprecipitate. Remaining, however, is a certain small amount of unreactedalki-earth aconitates, particularly calcium aconitate, which has thesame effect as if the starting material had been pure aconitic acidpartially neutralized by formation of small amounts of calcium aconitatetherein. In this case also, the amount of sulfuric acid added to theaconitate solution should be such as to produce a solution with a pHfrom 1 to 4. Example VII shows formation of some citraconic acid, due tothe presence of magnesium aconitate along with the calcium aconitate inth alkali-earth aconitate used as the starting material.

Having thus described the invention, what is claimed is:

A process comprising treating an aqueous suspension of an alkali earthaconitate with sulfuric acid in an amount less than chemicallyequivalent to the actions present in the aconitate but suflicient togive a pH from 1 to 4, thereby to convert most of the aconitates toaconitic acid leaving present a small quantity of the aconitates, andheating to decompose the aconitic acid in the 5 solution to itaconicacid and carbon dioxide in the Baker, J. Chem. 800.. (London), 1935,pages presence of the aconitates. 188-194.

Hawaiian Planters Record, vol. 47, 1943, pages EARL J. ROBERTS. 71-73.JOSEPH AMBLER- Miolati et 8.1,, Chemical Abstracts, Vol. 37, page ALFREDLAURENCE CURL. 5 [6247 (1943).

Umbdenstock et 111., Ind. 81 Eng. Chem, pages REFERENCES CITED 963467(1945) The following references are of record in the Ventre et 9.1.,Ind. 8: Eng. Chem., pages 201-204 file of this patent: 10 (1946).

